Oscillating circuits



Patented Apr. 29, 1952 OSCILLATING CIRCUITS Rene-Edouard Guillemant, Paris, France Application July 15, 1947, Serial No. 761,085 In France February 5, 1943 Section 1, Public Law 690, August 8, 1946 Patent expires February 5, 1963 9 Claims. 1.

My invention has for its object the improvement of tuning circuits for a wireless receiver set and more particularly although not exclusively for a superheterodyne receiver.

It is a well known fact that in the circuits generally used heretofore, the variation in tunin is obtained by varying the value of a condenser of variable capacity, the induction coil of the circuit retaining the same value for a given range of wave-lengths. Now, in contradistinction with such prior tuning means, my invention provides a circuit comprising an unvarying capacity and an induction coil, including an iron core and the value of which is modified through the sliding of the iron core inside the coil so as to cover the desired frequency range.

My invention has primarily for its object the production and formation of the induction coil allowing an easy mass production with the necessary accuracy.

My invention covers more particularly, but not exclusively, the production of such induction coils providing for a linear relationship between the axial shifting of the core and the frequency of the oscillating circuit; such a linear relationship allows as a matter of fact an adjustment of the circuit that is also easy throughout the extent of the range considered, which is an important advantage. It should however be noted that my invention is not limited to the obtaining of such a linear relationship as on the contrary it allows co-relating the displacement of the core with the frequency of the oscillating circuit.

In the case of a superheterodyne receiver, forming the most important application of my invention, the execution of the linear relationship ;f=aa:+b between the displacement at of the core and the frequency f of the circuit, a and b being constants, allows obtaining easily, as known in the art, a constant difference in frequency by means of a single control member. It is possible as a matter of fact in this case to mount two coils side by side with their axes parallel to one.

another without however saidcoils exerting any magnetic reaction with reference to one another, while the cores are secured to a common frame so as to be submitted to the same displacement at. In this case one of the induction coils may be made to satisfy the relationship f1=arv+b1 and the other the relationship j2=ax+b2, which leads to f1-f2=b1b2 sothat the difference in frequencies is independent of w and is consequently constant throughout the range considered I will now disclose myinvention with further 2 detail while referreing to the accompanying drawings showing by way of example and by no means in a limiting sense, a preferred embodiment. In said drawings:

Fig. 1 is a diagrammatic showing of an induction coil carrier according to my invention, the core being shown separate.

Fig. 2 shows part of a superheterodyne circuit employing this invention.

Fig. 3A shows a curve giving the relationship between the displacement a; of the core and the frequency f of the high frequency oscillating circuit and Fig. 3B shows a curve indicating the amount by which the difference in frequency between the high frequency and the heterodyne circuit differs from the accurate value of the intermediate frequency.

In Figs. 1 and 2, the same reference numbers correspond to the same members.

My invention includes chiefly the use of grooved coil supports so as to reliably obtain the indispensable regularity of production. The support considered is made of special Bakelite impregnated paper or the like material, the current leaks through which are low at high frequency; such material is known under the trade name Trolitul and it is illustrated cross-sectionally at I in Fig. 1. Said support is circular and is provided with grooves separated by partitions 3 provided with oblique grooves 9 for the passage of the wire H from one groove 2 to the next. My invention includes preferably the use of enamelled wire again with the purpose of al lowing a more regular production. In certain cases it may be an advantage to use multiple wire carefully pleated, such as Litzs Wire. The num ber of convolutions of the wire H1 in said grooves is defined beforehand so as to obtain the desired relationship, e. g. a rectilinear relationship between the displacement of the iron core 4 and the desired frequency to be obtained. This definition of the number of wires to be inserted into the different grooves may be compared to the usual construction including a fixed induction coil and a variable tuning condenser in which a similar accurate outlining of the condenser plates is provided. It will be readily apparent that this important feature provides a considerable adaptability in the present case and allows by reason of the comparatively large number of grooves 2 used, seven in the case illustrated, extremely strict matching between the actual curves obtained and the theoretical desired curve. Since there are as many independent variables available as there are grooves and the length of wire to be inserted in each groove may be defined if required down to one-half or even one-quarter of a convolution, if two or four oblique grooves 9 are provided between any two adjacent grooves, the construction of an induction coil having predetermined inductance-variation-with-core-displacement characteristics approaching the theoretical or ideal characteristics may be obtained. The use of grooved carriers for induction coils allows moreover obtaining a high regularity in production, i. e. it is possible to reduce the diiferences in tuning frequency between any two induction coils obtained in mass production down to admissible values, say less than 1 kilocycle, at any point in the frequency range considered. However, it is possible to match still more accurately the curve of a predetermined circuit with the curve of a prototype circuit through the following operation:

If the grooves are deeper than is required for the housing of the wires; after the laying of the wire and its impregnation according to the teachings of general technique, all or part of the free space remaining in the grooves is filled with magnetic material 8, which may for instance be dissolved in Trolitul and the like material and dried, so as to produce reliably at each point of the range a self-induction value above that of the prototype. It is then sufficient during the gauging to remove for instance on the lathe the excess of supplementary material to bring the induction coil to exact conformity with the predetermined prototype. The core 4 fits into the carrier I with the necessary clearance. Its sliding movement longitudinally of the axis of the coil is controlled through any suitable arrangement. The core is cylindrical and has a constant diameter throughout its height although it is possible if required to form a slight bevel on the inlet side facing the support for permitting insertion of the core into the coil support in a reliable manner in spite of the possible variations of position of the core with reference to that of the coil and similarly it is possible to provide a bevel 6 on the coil carrier on the inlet side facing the core.

The problem of the single control of the oscillating circuits to'be tuned to a same frequency is solved by my invention without difficulty and it is possible to locate side by side, with suitable screening therebetween a number of induction coils la and I2 equal to the number of circuits to be tuned and to secure their cores 4a and I3 to a common support and control knob [4 as shown in Fig. 2.

On the contrary, as disclosed hereinabove in the case of a superheterodyne receiver, it is necessary to provide oscillating circuits of a different frequency, that show a constant difference in frequency throughout the range. The method according to my invention allows reaching the desired results without any special difficulty by providing for each induction coil the suitable number of convolutions of wire in each groove; if required, it is possible to use for this purpose induction coils and iron cores of different diameters.

My invention allows obtaining in an advantageous manner the results referred to by applying the following features forming further objects of said invention:

(1) Use of two identical cores secured to the frame support so as to provide for a single control operation.

(ii) Use of two substantially identical supports for the induction coils in the high frequency and heterodyne circuits.

(iii) Use in the heterodyne circuit of a complementary constant induction coil inserted in series with the main induction coil. This complementary coil includes moreover the oscillation maintaining coil. This latter feature allows executing a comparatively constant coupling be tween the grid and anode circuits of the heterodyne, which condition is necessary as well known for a correct operation of the latter.

Fig. 2 is a diagram of the oscillating circuit of the heterodyne including a variable induction coil with its core 6a, the fixed condenser 5a and the complementary induction coil 6a associated moreover with the coil 1 connected to an oscillation generator to supply the oscillations.

It is a known fact that the oscillating circuit is generally inserted in the grid circuit of the oscillating member of the frequency changing stage and the oscillation maintaining coil is connected in the anode circuit of said element for generating the local oscillations.

Of course, the number of convolutions of wire in each groove of the variable induction coils of the high frequency and heterodyne oscillating circuits is defined so as to obtain a constant difierence in frequency. The complementary in duction coil 6a. may or may not include an iron core; in the first case, said core may be displaced to advantage through a thread connection so as to allow a final adjustment. It is advantageously of the same type as the variable induction coils, i. e. it may include a plurality of grooves each of which carries convolutions of the oscillating circuit and of the oscillation supplying induction coil so as to provide a sufficient coupling. Preferably there is no reaction between the main induction coil l and the complementary induction coil Ed, said result being provided by the relative positioning of said elements or a suitable screening. It is also possible to insert in separate grooves the convolutions of the complementary induction coil 6a and those of the oscillation supplying coil 1, for instance by winding these coils in alternate grooves in order always to provide for sufficient coupling between them.

The fixed capacities of the high frequency and intermediate frequency oscillating circuits assume preferably the same value. I will now disclose an example of. execution adapted for use in the case of a superheterodyne receiver.

Identical iron cores are used having a diameter of 8 mm. and a length of 22 mm. their total sliding stroke being equal to 23 mm. identical supports of variable induction coils are given an inner diameter of 8.2 mm. and the 11 grooves are identical; the diameter at the bottom of the grooves is 9.2 mm. while the outer diameter of the spool is 12 mm., the thickness of the partition is 0.4 mm. while the number of convolutions of the wire in each groove is as follows starting from the input into the core:

Induction coil of the high frequency circuit: 16-12-12-12-12--12-l8--12-3030-30.

Induction coil of the heterodyne: '7-5--'7-6- 54.'l58--'7-22.

Moreover the complementary induction coil 6a the support of which has a substantially smaller cross-sectional area than that of the variable induction coils is substantially shorter and includes only four grooves carrying respectively 2525-25 and 10 convolutions of wire for the oscillating circuit and 3030--300 convolutions for the oscillation supplying coil I; this latter induction coil includes no iron core.

The fixed tuning condensers are given the following values: 220 micromicrofarads for the heterodyne circuit and 212 micromicrofarads for the high frequency circuit.

The outer surface of the cores for the outermost position of said cores with reference to the coils lies at about 1 mm. from entrance surface of the coil. With these data, the variation in frequency of the high frequency oscillating circuit depending on the position of the core is given by the curve shown in Fig. 3A. In said figure, the displacements x of the core starting from its outermost position are given as abscissae and the frequencies of the circuit measured in kilocycles as ordinates.

It is apparent that there i obtained practically a linear relationship between one end of the range and the other, which range extends from 950 to 550 kc. Furthermore the shifting between the differences in frequency obtained between the signal high frequency and the heterodyne oscillating circuits and the value of the intermediate frequency which is 472 kc., is given by the curve shown in Fig. 3B, the frequency of the heterodyne circuit being higher by 472 kc. than the frequency of the high frequency circuit. The abscissae show the frequencies of the oscillations of the high frequency circuit measured in kilocycles while the ordinates give also in kilocycles the frequency shifting considered. The curve shows that the shifting is never above 2 kc., in other words the accuracy obtained i much higher than that given with the solutions generally applied heretofore, namely variable condensers, with padding and trimmer condensers. This result is by no means astonishing if it is remembered that the padding and trimmer condensers provide only two independent variables for cancelling the shifting, which cancellation can thu be obtained only for two points of the curve whereas the solution according to my invention provides the possibility of cancelling said shifting for a much larger number of points while at the same time a linear variation in frequency may be easily obtained. The use of a complementary induction coil 6a allows giving the coupling between the oscillating circuit and the oscillation supplying coil a value that is almost entirely independent of the location of the iron core of the variable induction coil, which would not be the case if the oscillation supplying coil 1 were located directly in the grooves carrying the variable induction coil I.

As already disclosed, it is not necessary for the high frequency circuit to have a linear variation for obtaining a constant intermediate frequency. If for any reason whatever, a different law of variation were adopted for said circuit, it is suficient to suitably calculate the variable induction coil of the heterodyne circuit in accordance with my improved method in order to reach the desired results.

It may at first sight be believed that the presence of the partitions between the grooves would give the curve shown in Fig. 3A the appearance of a staggered or stepped curve, but experience shows that this is not the case with the usual thickness given to the partitions.

Obviously, many modifications may be employed in the form of execution described with-v out unduly widening the cope of the present invention and I may in particular make use of induction coil supports wherein the grooves are given a breadth and a diameter varying from one groove to another.

My invention as claimed in the accompanying claims covers both the method of production described and the novel article of manufacture constituted by the induction coil and circuits obtained in accordance with said method.

What I claim is:

1. A variable iron core inductance coil comprising a substantially cylindrical hollow support having grooves formed in the outer surface thereof, a predetermined number of turns of wire in each of said grooves, said turns of wire being connected together so that a substantially linear relationship is obtained between the displacement of the variable iron core of the inductance coil and the frequency of the coil, and magnetic material filling at least part of the space around said turns of wire in said groove, said magnetic material being dimensioned to produce the desired relationship between the displacement of said iron core and the frequency of said coil.

2. A superheterodyne radio receiver including an oscillating heterodyne circuit and a high frequency signal circuit, a variable induction coil for each of said circuits of substantially identical construction, each of said induction coils comprising a tubular transversally grooved support, convolutions of wire in series with each of said circuits Wound in the successive one of said groove of said support and a magnetic core adapted to adjustably slide inside said support of each of said circuits, said grooves being spaced such that a substantially linear frequency response-core displacement characteristic is obtained in each of said circuits, and a single control for the cores of both of said induction coils for moving said cores to produce heterodyne 0scillations of a substantially constant frequency.

3. A variable iron core inductance coil comprising a substantially cylindrical hollow support having grooves formed in the outer surface thereof, a predetermined number of turns of wire in each of said grooves, said turns of wire being connected together so that a predetermined desired relationship is obtained between the displacement of the variable iron core of the inductance coil and the frequency of the coil, the magnetic material filling at least part of the space around said turns of wire in said groove, said magnetic material being dimensioned to produce the desired relationship between the displacement of said iron core and the frequency of said coil.

4. A superheterodyne radio received including an oscillating heterodyne circuit and a high frequency signal circuit, a variable induction coil for each of said circuits of substantially identical construction, each of said coils comprising a tubular transversely grooved support, a plurality of convolutions of wire in each of said transverse grooves, said convolutions of Wire being con nected in series, a magnetic core adapted to slide inside of each of said tubular supports, said grooves being so spaced and the number of said convolutions of Wire in different ones of said grooves being so proportioned that a substantially linear frequency change-core displacement characteristic is obtained in each of said circuits, and common control means for adjusting said cores to obtain the substantially linear frequency change in both of said circuits.

5. A superheterodyne radio receiver including an oscillating heterodyne circuit and a high frequency signal circuit, a variable induction coil for each of said circuits of substantially identical construction, each of said coils comprising a tubular transversely grooved support, a plurality of convolutions of wire in each of said transverse grooves, said convolutions of wire being connected in series, a magnetic core adapted to slide inside of each of said tubular supports, magnetic material filling at least part of the space around said turns of wire in said grooves, said magnetic material being dimensioned to produce the desired frequency change-core displacement characteristic in each of said circuits, and common control means for adjusting said cores to obtain the desired frequency change.

6. A superheterodyne radio receiver including an oscillating heterodyne circuit and a high frequency signal circuit, a variable induction coil for each of said circuits of substantially identical construction, each of said coils comprising a tubular transversely grooved support, a plurality of convolutions of wire in each of said transverse grooves, said convolutions of wire being connected in series, a magnetic core adapted to slide inside of each of said tubular supports, magnetic material filling at least part of the space around said turns of wire in said grooves, said magnetic material being dimensioned to produce the desired substantially linear frequency change-core displacement characteristic in each of said circuits, and common control means for adjusting said cores to obtain the substantially linear frequency change.

7 An oscillatory circuit the resonant frequency of which is adapted to be varied over a wide range comprising a substantially fixed capacitor and a variable inductance connected thereto, said variable inductance consisting of a hollow support having a plurality of grooves formed in a surface thereof, spacers for spacing said grooves, a coil composed of a number of turns disposed in each of said grooves, said turns all being connected in series, and a core of magnetic material adapted to be moved along the axis of said hollow support, said core being in the form of a cylinder having a cross section that is constant along its axis and the number of turns of wire disposed in said grooves following a predetermined law in order to obtain a substantially linear relation between the axial displacement of the core and changes in the reso nant frequency of the oscillatory circuit produced thereby.

8. An oscillatory circuit the resonant frequency of which is adapted to be varied over a wide range comprising a substantially fixed capacitor and a variable inductance connected thereto, said variable inductance consisting of a hollow support having a plurality of grooves formed in a surface thereof, spacers for spacing said grooves, a coil composed of a number of turns disposed in each of said grooves, and a core of magnetic material adapted to be moved along the axis of said hollow support, said core being in the form of a cylinder having a cross section that is constant along its axis and the number of turns of Wire disposed in said grooves following a predetermined law in order to obtain a substantially linear relation between the axial displacement of the core and changes in the resonant frequency of the oscillatory circuit produced thereby.

9. An oscillatory circuit the resonant frequency of which is adapted to be varied over a wide range comprising a substantially fixed capacitor and a variable inductance connected thereto, said variable inductance consisting of a hollow support having a plurality of grooves formed in a surface thereof, spacers for spacing said grooves, a coil composed of a number of turns disposed in each of said grooves, said turns all being connected in series, and a core of magnetic material adapted to be moved along the axis of said hollow support, said core being in the form of a cylinder having a cross section that is constant along its axis and the number of turns of wire disposed in at least one of said grooves located at the end of said support remote from the core-entering-end thereof, being substantially greater than the number of turns disposed in each of the other said grooves, the number of turns of wire disposed in said grooves following a predetermined law in order to obtain a substantially linear relation between the axial displacement of the core and changes in the resonant frequency of the oscillatory circuit produced thereby.

RENIi-EDQUARD GUILLEMANT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,671,106 Fisher May 29, 1928 2,340,749 Harvey Feb. 1, 1944 2,368,857 McClellan Feb. 6, 1945 2,394,391 Martowicz Feb. 5, 1946 FOREIGN PATENTS Number Country Date 252,285 Great Britain May 27, 1926 

